The invention relates to a domestic appliance for drying a damp product by means of a process air stream that can be conducted in a process air channel, said stream flowing through a treatment chamber comprising the product, a cooling assembly for cooling and condensing the process air stream once the latter has passed through the treatment chamber, the cooling assembly having a first heat exchanger, by means of which heat from the process air stream can be supplied to a working fluid, and a heating assembly for heating the process air stream before the latter flows through the treatment chamber, said heating assembly having a second heat exchanger by means of which heat from the working fluid can be supplied to the process air stream.
The invention also relates to a method for drying a damp product by means of a process air stream conducted in a process air channel, said process air stream flowing though a treatment chamber comprising the product, a cooling assembly for cooling the process air stream and condensing moisture from the process air stream once the latter has passed through the treatment chamber, and a heating assembly for heating the process air stream before the latter flows through the treatment chamber, heat from the air stream being supplied to a working fluid in the cooling assembly and heat from the working fluid being supplied to the process air stream in the heating assembly.
DE 40 23 000 C2, DE 197 38 735 C2 and WO 2006/029953 A1 each describe a domestic appliance in which the cooling assembly and the heating assembly form part of a heat pump in which some of the heat that is removed from the air stream in the cooling assembly is in any case supplied to the air stream again in the heating assembly.
According to DE 40 23 000 C2 a compressor heat pump is used in which a working medium (carbon dioxide or chlorinated and/or fluorinated hydrocarbon) is compressed into the gaseous state by a compressor, then liquefied in a first heat exchanger while emitting heat, then relieved of pressure as it passes through a throttle and is evaporated in a second heat exchanger by absorbing heat. Finally it returns to the compressor. According to DE 197 38 735 C2 a heat pump is used in which a first working medium (ammonia) is periodically absorbed and desorbed by a second working medium (water). According to document WO 2006/029953 A1 a heat pump is used in which thermoelectric elements, also called Peltier elements and constructed with special semi-conductor materials, act to conduct the heat.
A washing machine is known from DE 1 410 206 A in which laundry can be dried in addition to being washed. The document discloses several alternatives for the additional mechanisms that are required for this purpose. An electrical heating device for heating an air stream used for drying laundry can be provided along with a single heat exchanger for cooling the heated air stream following loading of the laundry, it being possible for the heater and the cooler to also form part of a heat pump device, however. The heat pump device can also be configured in such a way that it works with Peltier elements in order to utilize the thermoelectric effect.
A device, which emerges from an English excerpt belonging to the collection of data “Patent Abstracts of Japan” relating to JP 08 057 194 A, for drying laundry contains in its first channel system, in addition to a heater and a cooler which both form part of a thermoelectrically operated heat pump device, a further heat exchanger connected upstream of the cooler for cooling the air stream removed from the laundry, and an additional heating device connected downstream of the heater for additional heating of the air stream prior to loading of the laundry.
A Stirling process and a Vuilleumier process as examples of a regenerative gas cycle process are known from the document “Wärmetransformationsprozesse ohne Phasenumwandlung” [Heat transformation processes without phase conversion] by Dr Hans-Detlev Kühl, available on the internet since Nov. 26, 2006 under the address http://hdl.handle.net/2003/2798, see in particular pages 1 to 29. Each of these processes is suitable for use in a heat pump or a cooling device, applications in power engineering (for example in the heating of buildings) or for substance separation (in particular liquefaction and separation of air) being considered.
Reference is also made to U.S. Pat. No. 1,275,507 belonging to the inventor Rudolph Vuilleumier with regard to the Vuilleumier process.
In all generic domestic appliances with heat pumps which do not use the thermoelectric effect heat is absorbed and released in the working medium in phase transitions. Specific conditions relating to pressure and temperature must be adhered to for it to be possible to attain and effectively use the required phase transitions. This sometimes makes adjustment of the heat pumps to the temperature levels that are required in a domestic appliance difficult. The thermoelectric heat pump requires the use of special, expensive semi-conductor components and presents specific problems with regard to heat insulation and dry air conduction as heat can only be pumped over relatively short physical distances therein. This makes construction of a corresponding domestic appliance difficult. Furthermore, every known heat pump in a domestic appliance reaches the optimal operating conditions only relatively slowly on start-up. This results in an extended time requirement for a drying process, something which a user must regard as being very disadvantageous and not least of all because domestic appliances comprising heat pumps are conventionally sold at very high prices and are bought with high expectations accordingly.